Reduce default PoV size for XCM instructions

[Dinonard]

Pull Request Summary

Reduce default PoV size for XCM instructions.
This will soon be updated again with benchmarked values.

[github-actions]

Package	Line Rate	Branch Rate	Health
pallets/dapps-staking/src	81%	0%	✔
precompiles/dapps-staking/src	93%	0%	✔
pallets/ethereum-checked/src	48%	0%	❌
pallets/unified-accounts/src	80%	0%	✔
precompiles/utils/src	68%	0%	➖
precompiles/utils/src/testing	62%	0%	➖
chain-extensions/dapps-staking/src	0%	0%	❌
pallets/xc-asset-config/src	53%	0%	➖
chain-extensions/pallet-assets/src	0%	0%	❌
precompiles/assets-erc20/src	76%	0%	➖
precompiles/sr25519/src	79%	0%	➖
chain-extensions/xvm/src	0%	0%	❌
precompiles/utils/macro/src	0%	0%	❌
pallets/dapps-staking/src/pallet	85%	0%	✔
precompiles/batch/src	80%	0%	✔
chain-extensions/types/assets/src	0%	0%	❌
precompiles/substrate-ecdsa/src	78%	0%	➖
precompiles/xcm/src	84%	0%	✔
pallets/pallet-xcm/src	53%	0%	➖
primitives/src	62%	0%	➖
chain-extensions/types/dapps-staking/src	0%	0%	❌
pallets/contracts-migration/src	0%	0%	❌
precompiles/xvm/src	75%	0%	➖
primitives/src/xcm	66%	0%	➖
pallets/block-reward/src	85%	0%	✔
pallets/xvm/src	40%	0%	❌
chain-extensions/types/xvm/src	0%	0%	❌
pallets/collator-selection/src	69%	0%	➖
Summary	58% (2618 / 4545)	0% (0 / 0)	➖

Minimum allowed line rate is 50%